The present invention relates to a start-up circuit for providing a start-up voltage from a high voltage DC bus to a high voltage application circuit, for example, wherein the application circuit may comprise a switching regulator circuit coupled to a high voltage DC bus.
In the past, start-up circuits comprising external resistors are provided to application circuits wherein the application circuit comprises an integrated circuit. It is desirable to be able to eliminate the external resistor. However, this has been difficult to achieve in the past due to the high voltage. Further, it is also desirable to provide a start-up circuit which has an automatic shutoff feature which shuts down the start-up circuit when the voltage regulator output is sensed, i.e., when the voltage regulator output is generated by the voltage regulator circuit. In this way, maximum power dissipation is confined to a small time interval during start-up.
Further, it is desirable to be able to provide overcurrent protection that limits power dissipation in the start-up circuit in the event of an output short or overload condition.
As described previously, in the past, such start-up supplies were provided through an external resistor which increases cost and further which does not have the automatic shutoff capability nor overcurrent protection.
The main purpose of this circuit is to supply a switching voltage regulator with power upon start-up from a high voltage DC bus before the regulator can self-supply. A typical DC bus voltage may be approximately 600 volts, for example.